This invention relates to an apparatus and method for continuous variable reactive impedance control and, in particular, to an apparatus and method for continuous control over the reactive impedance of an oscillating circuit.
Oscillating circuits find application in many circumstances. An oscillating circuit may be any circuit that has one or more reactive components that influence the impedance of the circuit and, thus, the oscillation frequency or the natural resonant frequency of the circuit.
One such oscillating circuit includes an inductor and a capacitor. In one application, the oscillating circuit is employed as a transmitter of a magnetic inductive wave. In order to maximize the efficiency of the transmitter, the oscillating circuit incorporates the antenna as a part of the oscillating circuit. This arrangement is more efficient than driving the antenna.
A difficulty that may arise is that the value of the components that make up the oscillating circuit may drift. If the transmitter is operated at the natural resonant frequency of the components, this renders the frequency of the transmitter unstable. Alternatively, if the transmitter is driven at a predetermined oscillation frequency, the drift reduces the efficiency of the circuit since the natural resonant frequency will be different from the oscillation frequency.
Attempts have been made to provide an oscillating circuit with an adjustable frequency. For example, it has been suggested to switch tuning capacitors into the oscillating circuit so as to adjust the frequency in discreet steps.
The present invention provides an apparatus that has a continuously adjustable frequency, and a method for continuous adjustment of the reactive impedance of an oscillating circuit.
The apparatus and method according to the present invention feature a reactive component that is coupled to an oscillating circuit for a duration dt at the start of and before the end of each half-cycle of the oscillation frequency. The reactive component is decoupled from the oscillation circuit in between these two durations. By adjusting the duration dt, the impedance of the circuit is thereby adjustable. In a resonant circuit, this has the effect of adjusting the resonant frequency, and thus the oscillation frequency, over a continuous range of frequencies. In a driven circuit, this has the effect of adjusting the natural resonant frequency of the circuit, which impacts upon the efficiency of the circuit.
Further aspects and features of the present invention will be understood by those skilled in the art from a review of the following description of specific embodiments together with the accompanying drawings.